Block-cavity build 0.36ach test result!!

coillsaille

As has been said on here before, the traditional block built house still merits consideration for those aiming for passive levels of airtightness, if its done right.

My new build just had its air tightness test today and achieved .36ach.
Its a 2 storey (hollowcore) block build with a 250mm pumped cavity and triple glazing.

I knew the contractor had spent a lot of time on airtightness detailing, but I wasn't expecting a result like this.

The only slight leakage the tester could find was the two very large sliding patio doors (its impossible to get fully airtight sliding doors). If not for those sliders the result would have been even lower!

So for anyone thinking of building passive don't dismiss the blocks.:)

Clseeper

Coillsaille,

Very impressive result. I'm planing out a cavity build at the moment (two storey, hollowcore first etc) and had conservatively put in 1 ach into my provisional DEAP assessments.

Would you mind detailing how much work and the key features you focused on? From my reading so far, the key points are wrapping of the hollowcore in airtight membrane, sand & cement parge coat or wet plaster on inside wall, obvious roof and window details.

How did you find the chasing of the wall sockets and how that affected the air tightness?

Any other tips or hints would be appreciated.

sinnerboy

coillsaille wrote: »

My new build just had its air tightness test today and achieved .36ach.)

Can you clarify please - what was the Q50 Fabric Permeability result i.e. m3/m2/hr tested at 50 Pashcals

coillsaille

Clseeper, my knowledge of this stuff is very limited.
Until a year or so ago I hadn't even heard of airtightness and anything I have learnt in the meantime has been from spending many hours on this forum, and from the contractor who built my house. My lack of knowledge is why I engaged a building contractor who specialises in passive and near-passive builds.

I do know that, as you said, the hollowcore was wrapped and it was crucial that plastering was done right. Also airtight membrane was fixed to ceiling joists upstairs to seal off attic. Airtight tape played a big role from what I observed, every join was taped - around windows and doors, where walls meet raft and hollowcore and where ceiling membrane meets walls. As regards chasing the contractor had warned me before the electrician came on site to avoid chasing on external walls if possible. In some rooms this was unavoidable, so where sockets are located on external walls the chasing was done from floor up instead of from ceiling down and the cables will run through the screed floors. Also the chasing was sealed with a bonding coat, apparently plastering alone wont do.
That is the limit of my knowledge, if you want to know more PM me and I will give you contact details for the contractor.

coillsaille

Sinnerboy, I am completely clueless about this stuff. All I know is I was present for the test and was told the result. The guy doing the test said the initial result was .36. He said the final result may be slightly higher (something about feeding the data into computer back at his base) but he said it definitely wouldn't be above .38.
I doubt that answers your question, but I will ask my contractor to give me the breakdown of the final result when he gets it and will post same.

kieranhr

I completely agree - a block build house doesn't have to be leaky. Our block build houses generally hit a Q50 of below 3 with no airtight sealing technologies, no tapes or membranes, nothing fancier than a bit of flexible sealant around the window and door frames. (Way less when the client spends the money on tapes and membranes obviously.)

I know that a Q50 of 3 isn't very impressive for someone trying to build passive, but it's pretty good compared to the actual building regulation requirement of 7.

darragh_haven

Got my air tightness test result today. I was aiming for under 1.5 ach, i got 0.96ach. I would say "back of the net", but after seeing the OP's results, i'll walk away with my tail between my legs

coillsaille

Got the report today.
The n50 is 0.37
The q50 is 0.46
Will post details later as I am on the phone now.

sinnerboy

That is really good. This exceeds passive standard. Delighted for you.

beyondpassive

Excellent Result CoilleSaille, well done ND. Delighted to hear such results for wide cavity.

Can you clarify. The n50 is 0.37 ach's and the q50 is 0.46m3/hr/m2. That means the building volume number is higher than the surface area number, purely as a metric. So it would appear that the building has a large volume in a very compact envelope. Is this the case? When we talk in n50 metrics, we use the passivhaus interpretation of volume which excludes internal walls, service cavities, suspended ceilings and void spaces, the passivhaus volume is sometimes referred to as the visual volume.

A

coillsaille

Thanks beyondpassive.

I'm afraid your question is far too technical for my limited knowledge. Its quite a big house alright (353 m2), but I wouldn't call the envelope very compact.

According to the report:

Net floor area is 353 m2
Building volume is 1002 m3
Exposed surface area is 810 m2
N50 is 0.37 ac/h
Q50 is 0.46 m3/[h m2}

I don't know if that answers your question or not..